The present invention pertains to a sewing device with a programmable electronic control system for sewing folds and tucks.
In prior-art sewing devices of this type, the fabric being sewn is usually first delivered into a transfer position by a folding tool, which is provided on the front side with a replaceable guide tongue that is adapted to the course of the seam to be sewn where it is temporarily fixed in that position and subsequently held by a pressure pad by lowering this pressure pad. The feed of the fabric being sewn is subsequently performed by the pressure pad, which is displaced in the longitudinal direction as well as in the transverse direction and is likewise adapted in terms of its shape to the course of the seam. The sewing is performed along and as close to the pressure pad as possible, so that the pressure pad can be moved only away from the sewing needle to the outside during a transverse displacement movement.
The drawback of these prior-art sewing devices is, among other things, that not only the corresponding seam program, but also the parts whose shape depends on the course of the particular seam (pressure pad and guide tongue) must be replaced when changing the desired course of the seam. In addition, additional mechanical settings must be performed in case of a change in the fabric thickness, because the distance between the sewing needle and the folded edge of the fabric depends on the fabric thickness in the prior-art devices.
DE-GM 71 16 976 discloses a sewing device with a template rail driven in its longitudinal direction, which comprises a pressure pad for the fabric and a guide strip, which is continuously in contact with a guide means accommodated by a carrier in order to perform the movements which are directed sideways depending on the shape of the guide strip and which movements are superimposed to the longitudinal movement.
Therefore, not only the corresponding seam program but also the parts whose shape depends on the course of the particular seam (guide strip) must be replaced in case of a change in the desired course of the seam in this prior-art device as well.
This also applies to the sewing devices known from the documents DE 42 34 968 C1 and DE 40 31 200 A1 with a fabric holder driven in the longitudinal and transverse directions. These fabric holders, which are used to sew on pockets, have a sewing slot corresponding to the shape of the seam. Since the fabric holder grasps the pocket on both sides of the sewing slot it is carried without warping in unchanged aligned position in each transport direction.
When preparing tucks, in which the seam always ends at an acute angle at the folded edge of the fabric, the edge must be exposed. It is therefore not possible to use fabric holders which surround the seam to be formed for holding and guiding fabric that is to be provided with tucks.
Furthermore, a sewing unit for preparing tucks, which contains a folding tool movable between a receiving position and a transfer position for the fabric, an elastic folding aid plate, holding means in the form of a needle bar for the folded tuck, and a pressing rail for taking over the folded fabric and for guiding during the sewing operation, has been known from DE-PS 16 60 839. The angular position of the folding tool in relation to the pressing rail is adjustable in order to obtain a certain tuck depth. The folding tool pushes through the fabric during its forward movement under the elastic folding aid plate and the raised pressing rail to the extent that the tuck protrudes on the rear side of the pressing rail, doing so depending on the preselected angular position of the folding tool, i.e., corresponding to the desired tuck depth. At the end of the forward movement of the folding tool, the needle bar is moved downward, and its needles grasp the fabric in the area of the fold and fix it on a sewing table plate.
However, this document contains no reference to any means that determine the end of the feed motion of the folding tool, whether, e.g., any stops or the end point of the feed path of the drive means for the folding tool. The accurate setting of the end of the feed motion is of great significance, because the intersection of the tuck seam with the folded edge of the fabric is determined by the position or the distance of the end point of the feed motion of the folding tool from the needle of the sewing machine. The desired high-quality sewing result is obtained only if the end stitches of the seam, which are shortened for the purpose of securing the seam, have the required distance from the folded edge of the fabric. If the distance is too great, the tuck forms a rather unattractive, funnel-shaped depression instead of a sharp tip. If, by contrast, the distance is too short, the length of the tuck will be too short and some of the shortened end stitches fall into the free area, as a consequence of which the seam will not be sufficiently secured.
German patent application DE 100 11 162.9 discloses a sewing device with a sewing machine, a folding tool that can be moved between a receiving position and a transfer position for the fabric and a pressure pad for taking over the folded fabric and for guiding the fabric during the sewing operation, in sewing device stop means are provided for limiting the feed motion of the folding tool in the transfer position, and these stop means are located in the path of movement of the part of the folding edge of the folding tool that is surrounded by the folded fabric. It is achieved by means of the stop means arranged in this manner that the outside of the folded edge of the fabric will always have the same distance from the sewing needle in case of unchanged position of the stop means in case of thin and thick fabrics alike. However, regardless of the particular fabric thickness and without any corrective measures, the actual intersection, e.g., of a tuck seam, with the outside of the folded edge of the fabric always exactly coincides with the desired intersection.
The basic object of the present invention is to propose a sewing device of the type mentioned in the introduction, in which it is not necessary to change shape-dependent parts (guide tongue, pressure pad) in case of a change of the seam program and in which additional mechanical settings are not necessary despite a change in the fabric thickness.
According to the invention, a sewing device is provided with a programmable electronic control system for sewing folds and tucks. The sewing device comprises a sewing machine with a sewing needle and with a holding-down device and with a folding tool. The folding tool can be moved between a receiving position and a transfer position for the fabric. A stop is provided for limiting the feed motion of the folding tool in the transfer position. A holder is provided for the fold or tuck formed. A pressure pad is provided for taking over the folded fabric in the transfer position and for guiding the fabric during the sewing operation. The pressure pad has a straight design independently from the seam format. To obtain a flat sewing field, the pressure pad is arranged movably in the longitudinal direction by a first drive connected to the control system and in the transverse direction by a second drive connected to the control system. The control system can be programmed such that the particular desired seam course can be obtained exclusively by the superimposition of the longitudinal and transverse movements of the pressure pad. Both movements away from the sewing needle and movements toward the sewing needle are possible. The holding-down device is designed as a floating foot that holds the fabric flat at least in the area of the sewing needle.
The present invention is based on a device of the type described in DE 100 11 162.9 and it makes do without the use of a guide tongue that depends on the shape of the seam as well as of a shape-dependent pressure pad. The fabric is rather fed only with a folding tool with a straight folding edge and the fabric is held and guided during the sewing operation by means of a straight pressure pad, and the electronic control system is programmed such that the desired course of the seam is obtained exclusively by the superimposition of longitudinal and transverse movements of the pressure pad.
To make it possible to sew the largest possible number of different seam courses with the sewing device according to the present invention, it proved to be advantageous not to sew directly at the pressure pad but to select a greater mean distance between the sewing needle and the pressure pad than in prior-art devices, so that the pressure pad can perform both movements to the outside and toward the sewing needle. To avoid the problems that can possibly occur during the pulling out of the sewing needle, a holding-down device designed as a floating foot, which is located at a short distance above the folded edge of the fabric and holds the fabric during the pulling out of the needle and during the tightening of the thread knot without otherwise touching it is arranged in the area of the sewing needle.
To substantially shorten the changeover times of the sewing device even further during a change of the seam program, provisions are made in a preferred embodiment of the present invention for the seam parameters to be programmable in a graphics-supported manner. The sewing device contains for this purpose a display screen, which is electrically connected to the control system and on which the particular desired geometric seam course can be displayed. In addition, preferably standard seam programs are stored in the control system. In case of a change of a seam program, the particular new seam program is called up by depressing a corresponding key and the course of the seam is displayed on the display screen. If parameters of the seam program are to be changed, the corresponding new parameters are entered via a keyboard connected to the control system. All parameters of a seam course are defined now as length measurements.
To prevent the fabric from bulging out in the axial and radial directions, it proved to be advantageous for the floating foot to have both an opening, wedge-shaped course on its side facing the folded edge of the fabric and a course decreasing obliquely to the folded edge of the fabric on its front side opposite the direction of movement of the fabric.
In another embodiment of the present invention, the holding-down device is not fastened on the sewing machine of the sewing device according to the present invention, but on a part that also participates in the transverse movements of the pressure pad. The roller carrier of the drive displacing the pressure pad at right angles to the longitudinal direction has proved to be particularly suitable as such a part. Due to the joint movement of the holding-down device in the transverse direction, it can be designed as a holding-down device having such a large area that it covers the fabric area between the pressure pad and the edge of the fabric during the entire sewing operation and holds it flat as a result. Bulges which may frequently occur in the case of a holding-down device fastened to the sewing machine especially near the end of the given sewing operation due to the great distance existing between the holding-down device and the pressure pad are therefore eliminated in this case.
Provisions are made in another embodiment of the present invention for arranging a pressing finger, whose underside is flush with the underside of the pressure pad and which is offset transversely, at the pressure pad for the distortion-free transport of the fabric. The pressing finger preferably has a wedge-shaped cross section, so that the holding-down device seated on the pressing finger at the beginning of the sewing operation slides off from the pressing finger without a jerk as the sewing progresses.
Further details and advantages of the present invention appear from the following exemplary embodiments explained on the basis of figures. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.